PREPAKATION. 



C 631 ] 



PRESERVATION. 



upon a Tvater-of-Ayi* or some other stone, 

 and polishing them upon a clean leather 

 hone or strop with putty - powder and 

 water, finally upon a dry hone ahnie. 



Sections of very hard subsitances, as 

 agate, &c., are so easily made by jewellers, 

 that a description of the process is scarcely 

 necessary. They are cut by means of a 

 rotating' circular iron plate, its margins 

 being coated with a mixture of oil and 

 dianiond-dust. They are then ground upon 

 a plate of metal with emery-powder and 

 water, and polished upon a Hat surtace of 

 pitch with putty-powder and water. 



In grinding and polishing sections of 

 hard structures, it is often requisite to 

 cement them to a slide with Canada bal- 

 sam, heat being applied until the balsam 

 has become so hard as to fix the section 

 firmlv to the slide. As soon as one side 

 has been polished, the section is removed 

 from the slide, the balsam being rendered 

 soft by heat, the polished side cemented to 

 the glass, and tlie other side polished. The 

 balsam may afterwards be separated from 

 the section by maceration in oil of turpen- 

 tine, benzole, &c. 



The more delicate animal tissues require 

 hardening before section. This is usually 

 produced by freezing in the section-cutter ; 

 or by maceration in chromic-acid mixture 

 (15 grs. of chromic acid to the pint of 

 water, with ^ a pint of methylated spirit), 

 bichromate of potash (180 grs. to the pint), 

 osmic acid, or Miiller's liquid (composed of 

 220 grs. of bichromate of potash, 90 grs. of 

 sulphate of soda, and a pint of distilled 

 water). These liquids require to be poured 

 oft" and replaced until the tissue is suffi- 

 ciently hardened. 



Great care is required in the interpreta- 

 tion of the appearances presented by minute 

 objects or portions of tissue, as to the 

 intluence of the liquids in which they are 

 immersed ; even water often totally distorts 

 their natural appearance, as in the case of 

 pollen. Sec. And in animal tissues, the 

 liquid of the allautois, blood-serum, or 

 iodized serum or albumen (p. 441), are 

 often useful as con-espouding nearly to the 

 liquid in which they are naturally im- 

 mersed, and so producino' but httle change. 



Besides these methods of preparation, 

 there are those which enable the observer 

 to keep sections or minute plants and animals 

 under continuous examination without be- 

 coming dry, to provide a proper and equable 

 or even higher temperatures to parts or the 



whole of organisms, and to add gases to the 

 fluid surrounding the object. Reckling- 

 hausen's moist chamber fullils tlie first 

 requirement ; and Strieker's slide, which is 

 heated b}^ means of the galvanic current, is 

 most useful in producing constant anu)unt3 

 of heat. Strieker's gas-chamber, slide, and 

 its conducting tubes enable carbonic acid, 

 oxygen, liydrochl )ric acid, or any t)ther gas 

 to be applied to the fluid under examination. 

 A substitute for those complicated pieces of 

 apparatus, may be made by procuring a flat 

 strap-shaped piece of metal, to be fixed upen 

 the stage, witli an aperture near one end corre- 

 sponding with that in the stage. The sUde 

 is placed upon this, and a feeble flame of a 

 spirit-lamp applied to the other end, will 

 serve to produce the gentle heat required to 

 set in motion or continue the amoeboid 

 movements of organisms. 



The preparation of many objects requires 

 the process of dyeing or Staining. 



BiBL. Beale, ffotv Sfc. ; Carpenter, Mi- 

 croscvpe ; Frey, Mikr. ; Strieker, Hist. ; 

 Gerlach, i6«Z. ; Rutherford, 7/?'s^. ; Mouchet, 

 Mn. Mic. J. iii. 75 ; Flemming, ScJmltze's 

 Archiv, ix. 123 ; Gronland, Cornu, and 

 Rivet, Prep. Micros. {Botanicul), 1871, Qu. 

 Mic. Jn. 1872, 82; L. Clarke, Phil. Tr. 

 18ol ; Minot, Mn. M. J. xviii. 97 ; Meyer, 

 Arch. Mik. An. xiii.; Moseley, Qu. Mic. Jn. 

 1872, 374, 379; Pritchard, Qu. Mic. Jn. 

 1872, 380; Ranvier, Hid. tech.; Marsh, 

 Section-cuHing ; Betz, Schultze\s Archiv, '\x. 

 101 ; Qu. Mic. Jn. 1873, 343 ; Gibbs, Hist. 

 1880. 



PRESERVATION of microscopic ob- 

 jects. — Under this head we shall consider 

 the arrangement of microscopic objects for 

 permanent preservation, supposing that they 

 have been prepared (Prepaeation) in 

 such manner as to render this possible. 



Dry objects, or those which exhibit their 

 structural peculiarities in the dry state. — 

 These are sometimes mounted alone, at 

 others when immersed in some preservative 

 compound. 



In the dry and uncovered .state, they are 

 occasionally mounted upon disks of cork, 

 leather, or pasteboard, the surface upon 

 which the object is to be placed being black- 

 ened by a coating of very fine lamp-black 

 mixed with warm sfze or gum-water, or by 

 a piece of dull black paper pasted upon it ; 

 the simplest way of making the disks is to 

 paste black paper upon thick soft leather, 

 and cut out the disks with a punch, like gun- 

 wads. The object is fastened to the disk with 



